The present disclosure relates to solid-state imaging devices. More particularly, the present disclosure relates to a CMOS solid-state imaging device, a method of driving the CMOS solid-state imaging device, and an electronic system using the CMOS solid-state imaging device.
To date, in a general CMOS solid-state imaging device, a method of reading signal charges, which have been generated and accumulated by light receiving sections of individual pixels disposed in a two-dimensional matrix, for each row in sequence has been employed. In this case, exposure time of the light receiving sections of the individual pixels is determined by a start and an end of readout of signal charges, and thus exposure timing differs for each pixel. Accordingly, if an image of a fast-moving subject is captured using such a CMOS solid-state imaging device, there has been a problem in that the image of the subject is deformed.
In order to address the above-described problem, in recent years, proposals have been made on a simultaneous image capturing function (global shutter function) for achieving uniformity in accumulating period. Also, CMOS solid-state imaging devices having a global shutter function have been expanding in application.
In a CMOS solid-state imaging device having a global shutter function, in order to accumulate signal charges generated by a light receiving section until readout time, it is normally necessary to have a charge accumulation section with a light-shielding effect. For the charge accumulation section, there are many normal CMOS solid-state imaging devices that use a floating diffusion section, which is originally disposed for a pixel. Also, Japanese Unexamined Patent Application Publication No. 2009-268083 has disclosed a configuration of using two sections, namely a CCD-type charge holding capacitor section and a floating diffusion section for a charge accumulation section in order to increase a number of saturated electrons.
Incidentally, the CCD-type charge holding capacitor section described in Japanese Unexamined Patent Application Publication No. 2009-268083 is also used for a receiver of signal charges that has overflowed from a photodiode during an exposure period. Accordingly, exposure is not allowed while the charge holding capacitor section holds signal charges. Accordingly, exposure is allowed only after signal charges of all the pixels are read out. Thus, there has been a problem in that there are many periods in which exposure is not allowed, a smooth moving image that demands continuous exposure is not allowed, and sensitivity of a moving image is deteriorated.